1. Field of the Invention
The present invention relates to the field of displaying technology, and in particular to a liquid crystal display device and a method for manufacturing a light guide plate (LGP) positioning block thereof.
2. The Related Arts
Liquid crystal displays (LCDs) have a variety of advantages, such as thin device body, low power consumption, and being free of radiation, and are thus used widely, such as mobile phones, personal digital assistants (PDAs), digital cameras, computer monitors, and notebook computer screens.
Most of the LCDs that are currently available in the market are backlighting LCDs, which comprise an enclosure, a liquid crystal panel arranged in the enclosure, and a backlight module mounted in the enclosure. Since the liquid crystal panel is not self-luminous, light supplied from the backlight module is necessary for normally displaying an image. Thus, the backlight module is one of the key components of a liquid crystal display. The backlight modules can be classified as a side-edge backlight module and a direct backlight module, according to the site where light gets incident. The direct backlight module comprises a light source, such as a cold cathode fluorescent lamp (CCFL) or a light-emitting diode (LED), which is arranged at the backside of the liquid crystal panel to directly form a planar light source supplied to the liquid crystal panel. The side-edge backlight module comprises an LED light bar, serving as a backlight source, which is arranged at an edge of a backplane to be located rearward of one side of the liquid crystal panel. The LED light bar emits light that enters a light guide plate (LGP) through a light incident face at one side of the light guide plate and is projected out of a light emergence face of the light guide plate, after being reflected and diffused, to pass through an optic film assembly so as to form a planar light source for the liquid crystal panel.
The LGP is one of the important components of a liquid crystal display and is often made of poly(methyl methacrylate) (PMMA), which is also referred to as “organic glass” and has the property of thermal expansion. When a liquid crystal display is operating in a high temperature, the LGP gets expanded; and for operation in a low temperature, the LGP contracts. The size difference between expanding and contracting might as large as millimeters. On the other hand, positional accuracy between the LGP and the backlight source affects, to a great extent, the image style of the liquid crystal display.
FIG. 1 is an exploded view showing a conventional liquid crystal display device and FIG. 2 is a top plan view showing a backlight module of the conventional liquid crystal display device. With reference to FIGS. 1 and 2, the conventional liquid crystal display device comprises a backlight module 10 that is composed of a backplane 100, a light-emitting diode (LED) light bar 200, a light guide plate 300, and an optic film assembly 400, a mold frame 500 arranged on the backlight module 10, a liquid crystal panel 600 arranged on the mold frame 500, and a bezel 700 arranged on the liquid crystal panel 600. The light guide plate 300 comprises positioning posts 800 arranged adjacent to a light-entrance side of the LED light bar 200 to maintain a light coupling distance between the light guide plate 300 and the LED light bar 200, while elastic positioning blocks 900 are arranged at the side of the light guide plate 300 that is distant from the LED light bar 200 to achieve positioning.
As shown in FIG. 3, in a normal temperature, a proper gap is present between the side of the light guide plate 300 that is distant from the LED light bar 200 and the positioning blocks 900 to facilitate assembly and accommodate manufacturing tolerances.
As shown in FIG. 4, when the liquid crystal display device is in a high temperature, the light guide plate 300 that is heated and thus expanded gets into contact with the positioning blocks 900. Since the positioning blocks 900 are made of a solid elastic material and thus possess elasticity, they can absorb the increased size of the light guide plate 300 caused by expansion so as to maintain stable and tight engagement between the light guide plate 300 and the positioning blocks 900.
However, as shown in FIG. 5, when the liquid crystal display device is in a low temperature, the light guide plate 300 is cooled and gets contracted so that the gap between the light guide plate 300 and the positioning blocks 900 is enlarged. Under this condition, the positioning blocks 900 do not provide the function of effective positioning so that the light guide plate 300 may readily separate and break due to actions caused by vibrations and impacts.